The present invention relates to a device for use in purifying air contaminated with sulfur compounds or other gaseous contaminants, whereby the device is well suited for use in a manhole or similar structure. More particularly, the present invention relates to a device for holding an amount of gas filtration media, whereby the preferred design for the device causes the contaminated air to enter through the side of the device and exit through the top of the device.
Manholes, or similar structures, are used to access underground utility and sewage systems, with the manhole serving as a conduit to the surface. Often these underground systems will accumulate significant amounts of organic waste and moisture, with such conditions ideal for the propagation of bacteria. It is known that some species of bacteria that readily propagate under such conditions will metabolize organic waste. Byproducts of the metabolic process include hydrogen sulfide gas and other gaseous contaminants, which result in odors emanating from a sewer system. The odors exit through the manhole. Besides causing a foul smell, these waste products can cause corrosion of the concrete walls which form the manhole. As such, it is desired to have a method and/or device for eliminating or treating air so as to remove such gases and waste byproducts. More importantly, it is desired to have a method or device for preventing or reducing the presence of undesired odors exiting a manhole.
One method for controlling the diffusion of various odiferous gases is to seal the manhole cover to prevent the escape of the fouled air from a sewer or utility system. Sealing traps the air contaminated with the various gases in the manhole. Unfortunately, this allows for the likely buildup of methane and hydrogen sulfide, aggravates corrosion problems, and creates a hazardous environment.
In response, devices have been developed which allow for the free exchange of gases between the sewer or utility system and the surface. An example of such a device is a biofilter or activated carbon container located just below the manhole lid. It is an air permeable basket that holds filter media within the confines of the basket. The biofilter is positioned within the neck of the manhole and is typically fastened or attached to the neck. Fastening usually results from having the device bolted or attached to the wall of the manhole neck. The biofilter basket device is designed such that the contaminated air enters through the bottom of the basket and flows upward to pass through the filter media and exit the top of the basket.
The design of the activated carbon and biofilter basket device is disadvantageous for a number of reasons. For one, debris can collect in the space between the device and the manhole lid. This diverts surface water, which readily enters the manhole, to flow towards the interior of the basket. Resultingly, the water typically passes through the device. There are no means for diverting the path of the water so that the water must pass through the device. Often during a heavy rain storm, large volumes of water will pass through portions of the manhole basket device and into the sewer system. Passage of the water through the device causes the media to be washed away or ruined. Even more problematic is that the water can cause channeling within the filtration media found in the basket. Channeling decreases the effectiveness of the media by creating holes or passages through which non-filtered air can pass. The loss of media and/or media contamination prevents adequate filtering of contaminated gas by the media. The activated carbon basket filtration devices, generally, work well in dry locales, but when substantial rainfall is received, such devices are found to be inadequate. For this reason, it is desired to have a device that can be used to filter contaminated air in regions where there is rainfall exceeding that of an arid region.
Another problem is that, often, a small space is formed between the outer wall of the device and the manhole neck. Typically, not all of the air is treated because some of the contaminated air can pass through the space located between the basket and the manhole neck. For this reason, a device that inhibits the escape of non-filtered air and filters most all of the contaminated air is desired.
Devices have been developed which include a lid to divert water away from the media and a valve to allow for the escape of the diverted water. Regardless of whether fouling of the media is prevented, all filtration devices are limited generally by the amount of media they can hold. When filtering air in a manhole or similar structure, there is only a limited amount of pressure available to force or xe2x80x9cpushxe2x80x9d the contaminated air to pass through the filtration media. Air pressure is the force that pushes the air through the media. As the air passes through the filter media a pressure drop occurs. This means the pressure decreases, causing less force to be applied to the gas or air, so that the air will pass through a limited amount of filtration media and will only travel a certain distance before there is insufficient pressure to push the air any further. If the distance of the media through which the air must pass is too great, the purified air will not easily exit the media.
Most prior art gas filtration devices are of a limited length because of concerns regarding pressure drop of air or gas. When air flows upward, it can pass through only a limited amount of filter media before a pressure drop occurs. It is desired, however, to have a device that contains a greater amount of filtration media and is of a longer length than most prior art devices. Such device, however, must be able to filter air without the attendant problems associated with pressure drop.
Other odor control devices involve placement of above ground containers outside of the manhole, either directly on top of or adjacent to the manhole. Manholes, however, are often placed in streets or other high traffic areas that do not allow for use of above ground devices. Thus, the device should be one that can be placed under the manhole cover.
As such, it is desired to have a device that can be used in all geographic regions regardless of the amount of rainfall. A device that does not allow debris trapped in the manhole neck to damage the filtration media is also desired. The device should be designed such that the media will not be washed away or channeled. Additionally, it is desired to have a device that forces all, or the majority, of the air to be filtered by the media so that the contaminated air does not flow around the sides of the device. Another desire is to have a system that can hold a comparatively significant amount of media. It is further preferred if devices for use in a manhole can have a longer construction. Most importantly, it is desired to have a device whereby a pressure drop is not a concern, and whereby exhaust gas from the sewer and air from the outside easily flows through the device.
The present invention relates to a device designed and dimensioned for holding an amount of media for use in filtering contaminants from air. More preferably, the present invention relates to a device for use in a manhole or similar structure, whereby the device can be placed in the manhole and used to filter air contaminated with sulfur and other contaminants found in a sewer or similar system.
The filtration device can have a variety of different constructions as long as an amount of filtration media can be held so that contaminated air can be filtered. A preferred construct results in the air following an S-shaped path during the treatment process. As the contaminated air collects in the manhole, pressure increases which in turn pushes the contaminated air upward and then horizontally through the filtration media. The present invention is designed so that instead of the air flowing in a continues upward path, it flows in a horizontal path (of relatively short duration) through the filtration media. This is advantageous because more filtration media can be placed in the device without increasing pressure drop. Essentially, the air follows a path that is S-shaped so that the air flows vertically, then horizontally, and finally vertically. This construction causes the contaminated air to travel over the filter media according to a reverse radial flow path. In the present case, radial flow means the air to be filtered travels in a substantially horizontal path, from the outside inward.
The filtration device will include a member for holding the filtration media, with the member being substantially air permeable. The contaminated air passes through an air permeable member wall and contacts the filtration media held by the member. Located within the member will be an air permeable conduit, which permits the escape of the air after it has been filtered. The conduit forms a channel through the filtration media, which allows for the purified air to exit. The filtration media will occupy the space between the wall and the conduit. Importantly, the member has a construction that allows for the contaminated air to be purified by passing over and through the filtration media, with the purified air then exiting through the conduit and out of the device. The member must further be of a construction whereby a significant pressure drop does not occur as the air passes through the media so as to allow the purified air to reach the conduit and exit the device. The member, as well as the device, in total, can be of any size, as long as air is filtered.
The present device is preferably used in a manhole or similar contained structure. The preferred construction of the filtration device is a cylinder-shaped member having a gas permeable wall and the conduit located within the member. The cylinder-shaped member preferably has a bottom that can be opened and closed. An annular collar is preferably integrally attached to the cylindrical-shaped member opposite the bottom. It is further preferred for the bottom portion of the filtration device to be of a solid, non-gas permeable construction. The bottom portion is attached to the cylinder member and closes the device, with it desired for the bottom to be hinged so it can be opened and closed.
To support the filtration device in the manhole, it is preferred to use a tub design to hold the filtration device in an elevated position. Preferably, the filtration device includes outward extending tabs or an annular ring, which will be receivably held by an inward extending annular ring or tabs affixed to the tub. Oppositely, the tub will then be supported by the lip of the manhole, whereby the tub has an outward extending member, which is received and held by the lip of the manhole.
The present invention is advantageous because it allows for reverse radial flow treatment of contaminated air (out) and outside air (in). It is also advantageous because it can hold a greater amount of media than most similar devices. There is less concern regarding a pressure drop when the air is being filtered because the design of the present device does not result in the air having to travel comparatively long distances over the media. The device is further advantageous because it is not subject to damage or media malfunction as a result of a rain storm. The device is also advantageous because it can be readily adjusted and easily removed and reset. Finally, the device is advantageous because it is well suited for use in a manhole.